School principals fear they could soon be powerless to confiscate weapons and illicit drugs from pupils, under changes to the Education Act.

The Education Amendment Bill, now before Parliament, includes changes to the surrender, retention, search and seizure powers held by schools.

Under the proposed changes, teachers would not be allowed to search pupils or their property but would be able to search property owned by the school, such as lockers and desks.

Dogs would no longer be allowed to search schools for drugs, and schools would not be able to test pupils for drug use.

Schools could suspend pupils for refusing to hand over a weapon or drugs.

Wellington College headmaster Roger Moses said the impact of the bill was still unclear, but any move to reduce schools' ability to search and seize could make them less safe.

"If contraband of any kind is brought into the school we want the ability to search for that stuff. It is going to make it more difficult for schools to police internally."

New Zealand Secondary Principals' Council chairman Allan Vester said the rules on searching pupils had been "clarified" to the point where teachers would not be able to search pupils at all.

"This effectively meant if a teacher saw a student putting a knife, drugs or stolen property in their bags and asked them to hand it over, the student could just say ‘no'," he said.

"If you know a student has a weapon, they won't hand it over and the police don't arrive in time, then they are leaving the site carrying something you know is a weapon."

Principals would probably take the law into their own hands for the safety of other pupils and staff, he said.

"If it is the difference between breaking the law and someone being stabbed, I am sure principals will step in for the safety of their students and staff and break the law," he said.

"In those cases, many principals will break the law, seize the bag and lock it up."

Shirley Boys' High School principal John Laurenson said the bill was unlikely to change the school's existing search procedure, but he was concerned about not being able to bring drug dogs through the school.

Shirley, in Christchurch, is searched twice a year by drug dogs.

"We see that as a deterrent," Mr Laurenson said.

"The boys know it is happening; they just don't know when it will be.

"It sends a clear warning to students that that type of behaviour is not permitted."

New Zealand Principals' Federation president Paul Drummond said the amendment had been scrutinised by secondary principals, who wanted to balance the rights of pupils with the safety of the wider school community.